When steel or stainless steel tubes or bars are severed using an appropriate coated cutting tool or cutting tool insert, the cutting edge is frictionally heated to a high temperature with the consequence that the material being cut becomes welded onto the cutting edge of the cutting tool insert. As a result, the coating can flake and small cemented carbide chips can be torn out of the cutting tool or cutting tool insert substrate body.
On the other hand, for grooving of the same materials, a high coating wear resistance in combination with a stiff substrate material is required. Finding a cutting tool material that effectively fulfils both these requirements is a challenge.
So far it has been very difficult to improve all tool properties simultaneously. Commercial cemented carbide grades have therefore been optimised with respect to one or few of the wear types and hence to specific application areas.
Swedish patent application 9602413-8 discloses a coated cutting insert particularly suited for wet turning or grooving stainless steel components. The inserts are characterised by a cemented carbide body consisting of WC--Co and cubic carbides coated by one layer of TiC.sub.x N.sub.y O.sub.z with columnar grains, one layer of smooth, fine grained .kappa.--Al.sub.2 O.sub.3, and preferably an outer layer of TiN.
Swedish patent application 9504304-8 discloses a coated cutting insert particularly useful for wet and dry milling of low and medium alloyed steels. The insert is characterised by a cemented carbide substrate consisting of Co--WC and cubic carbides, a coating including a layer of TiC.sub.x N.sub.y O.sub.z with columnar grains, a layer of smooth, fine grained .kappa.-Al.sub.2 O.sub.3 and preferably an outer layer of TiN.